Re: Re: [PATCH v2] arm64: add check_wx_pages debugfs for CHECK_WX

[Phong Tran <tranmanphong@gmail.com>]

On 4/22/20 10:26 PM, Will Deacon wrote:
> On Wed, Apr 22, 2020 at 03:35:27PM +0100, Mark Rutland wrote:
>> On Wed, Apr 22, 2020 at 12:35:58AM +0700, Phong Tran wrote:
>>> follow the suggestion from
>>> https://github.com/KSPP/linux/issues/35
>>>
>>> Signed-off-by: Phong Tran <tranmanphong@gmail.com>
>>> ---
>>> Change since v1:
>>> - Update the Kconfig help text
>>> - Don't check the return value of debugfs_create_file()
>>> - Tested on QEMU aarch64
>>
>> As on v1, I think that this should be generic across all architectures
>> with CONFIG_DEBUG_WX. Adding this only on arm64 under
>> CONFIG_PTDUMP_DEBUGFS (which does not generally imply a WX check)
>> doesn't seem right.
>>
>> Maybe we need a new ARCH_HAS_CHECK_WX config to make that simpler, but
>> that seems simple to me.
> 
> Agreed. When I asked about respinning, I assumed this would be done in
> generic code as you requested on the first version. Phong -- do you think
> you can take a look at that, please?
> 

sure, plan to make change in mm/ptdump.c with KConfig 
"ARCH_HAS_CHECK_WX" as suggestion.

Then need align with this patch in PowerPC arch also

https://lore.kernel.org/kernel-hardening/20200402084053.188537-3-ruscur@russell.cc/

diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
index a1efa246c9ed..50f18e7ff2ae 100644
--- a/arch/arm64/Kconfig.debug
+++ b/arch/arm64/Kconfig.debug
@@ -25,6 +25,7 @@ config ARM64_RANDOMIZE_TEXT_OFFSET

  config DEBUG_WX
         bool "Warn on W+X mappings at boot"
+       select ARCH_HAS_CHECK_WX
         select PTDUMP_CORE
         ---help---
           Generate a warning if any W+X mappings are found at boot.
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 0271b22e063f..40c9ac5a4db2 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -138,3 +138,6 @@ config PTDUMP_DEBUGFS
           kernel.

           If in doubt, say N.
+
+config ARCH_HAS_CHECK_WX
+       bool
diff --git a/mm/ptdump.c b/mm/ptdump.c
index 26208d0d03b7..8f54db007aaa 100644
--- a/mm/ptdump.c
+++ b/mm/ptdump.c
@@ -137,3 +137,29 @@ void ptdump_walk_pgd(struct ptdump_state *st, 
struct mm_struct *mm, pgd_t *pgd)
         /* Flush out the last page */
         st->note_page(st, 0, -1, 0);
  }
+
+#ifdef CONFIG_ARCH_HAS_CHECK_WX
+#include <linux/debugfs.h>
+#include <asm/ptdump.h>
+
+static int check_wx_debugfs_set(void *data, u64 val)
+{
+       if (val != 1ULL)
+               return -EINVAL;
+
+       ptdump_check_wx();
+
+       return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(check_wx_fops, NULL, check_wx_debugfs_set, 
"%llu\n");
+
+static int ptdump_debugfs_check_wx_init(void)
+{
+       debugfs_create_file("check_wx_pages", 0200, NULL,
+                       NULL, &check_wx_fops) ? 0 : -ENOMEM;
+       return 0;
+}
+
+device_initcall(ptdump_debugfs_check_wx_init);
+#endif


Regards,
Phong.